This invention relates to magnetohydrodynamic generators and, more specifically, to an improved gaseous electrode for such generators.
MHD generators produce electrical power by motion of a high temperature electrically-conductive gas through a magnetic field. This movement induces an electromotive force between opposed electrodes within the generator. The rapid motion of the high temperature gases, however, seriously erodes the generator's electrodes as do internal electric arcs which connect the MHD generator's main plasma stream to a load. Although gaseous electrodes have been suggested in the past, it is an object of this invention to provide an improved gaseous electrode using an electrically conducting gas which does not wear out even though subjected to high generator current densities.
Gaseous electrodes have previously been suggested wherein an arc is caused to move from place to place within a cavity along one or more openings in the electrode, thereby causing ionized gas to fill the entire cavity and be forced into the generator's main channel. Such structures have been described as employing a cathode spot phenomenon according to which the MHD magnetic field causes the arc to move about the inner electrode. It has also been suggested that longitudinal movement of the arc can be controlled by the magnetic field set up by a coil which is wrapped around the electrode. Such structures, however, have not necessarily been as simple or reliable as might sometimes be desired. Hence, it is an object of this invention to provide a gaseous electrode having controlled movement of the arc in both circumferential and longitudinal directions without the requirement of a field-producing coil.
It has also been found that an arc oscillating longitudinally along an inner electrode element of a gaseous electrode can cause erosion of the internal electrode element in the area where the longitudinal arc movement is reversed. Consequently, it is another object of this invention to provide a gaseous electrode which substantially eliminates the problem of erosion on the inner electrode.